This invention relates to zig zag sewing machines, and in particular, zig zag sewing machines capable of automatically producing buttonholes of various sizes.
There are many different types of automatic buttonhole mechanisms on sewing machines. With the increasing use of electrical devices for controlling, or actuating, the sewing machine stitch forming instrumentalities, electrical switches are replacing mechanical linkages for effecting different state changes in the various operating mechanisms, as, for example, the buttonhole mechanism. The use of electrical switches, however, fosters a new, or more acute, problem area. The environment in which a sewing machine operates contains a high degree of contaminates in the form of lint particles. These particles are dielectric in nature and tend to collect on the switch contacts causing spotty electrical operation or complete failure of the switches.
U.S. Pat. No. 3,113,537 of Bona discloses one embodiment of a buttonhole mechanism in which the control mechanism therefor employs the breaking of a light beam to a photoelectric sensor to achieve a switching. While this arrangement may eliminate electrical failure to contact contamination, it nevertheless is susceptible to contaminant failure when the light is impeded from impinging the sensor due to a layer of contaminants.